Shock absorbers are used in conjunction with automotive suspension systems and with other suspension systems to absorb unwanted vibrations which occur during movement of the suspension system. In order to absorb these unwanted vibrations, automotive shock absorbers are generally connected between the sprung mass (body) and the unsprung mass (suspension) of the automobile.
One of the most common type of shock absorbers for automobiles is the dual tube dashpot type. These shock absorbers have a piston which is located within a pressure tube. The piston is typically connected to the sprung mass of the vehicle using a piston rod. The piston divides the pressure tube into an upper working chamber and a lower working chamber. Because the piston, through valving, has the ability to limit the flow of damping fluid from the upper working chamber to the lower working chamber within the pressure tube when the shock absorber is extended, the shock absorber is able to produce a damping force which counteracts the vibrations which would otherwise be transmitted from the unsprung mass to the sprung mass during the extension stroke. In the dual tube shock absorber, a fluid reservoir chamber is defined between the pressure tube and a reservoir tube which is positioned around the pressure tube. A base valve assembly is located between the lower working chamber and the reservoir chamber. Because the base valve assembly, through valving, has the ability to limit the flow of damping fluid from the lower working chamber to the reservoir chamber when the shock absorber is compressed, the shock absorber is able to produce a damping force which counteracts the vibrations which would otherwise be transmitted from the unsprung mass to the sprung mass during the compression stroke.
Because the piston rod of the shock absorber extends only through the upper working chamber and not through the lower working chamber, movement of the piston with respect to the pressure tube causes a difference in the amount of fluid displaced in the upper working chamber from the amount of fluid displaced in the lower working chamber. This difference in the amount of fluid displaced is known as the rod volume and it flows through the base valve assembly during both the extension stroke and the compression smoke.
When the shock absorber extends in length, extension stroke, fluid flows through valving in the piston from the upper working chamber to the lower working chamber to create the damping force but an additional volume of fluid is needed in lower working chamber due to the rod volume concept. Thus, fluid will flow from the reservoir chamber to the lower working chamber through a check valve located within the base valve assembly. The check valve does not generate a damping force.
When the shock absorber compresses in length, compression stroke, fluid flows through a check valve in the piston from the lower working chamber to the upper working chamber. The flow through the check valve does not generate a damping force. Due to the rod volume concept, an additional volume of fluid must be removed from the lower working chamber. Thus, fluid will flow from the lower working chamber to the reservoir chamber through valving in the base valve assembly to create the damping force.
In some applications, the continuous flow of fluid into and out of the reservoir chamber through the base valve assembly has led to aeration of the damping fluid. In order to decrease the aeration of the damping fluid, baffle springs have been designed for the reservoir chamber. These prior art baffle springs typically are in the form of a helical spring which is disposed on the pressure tube to extend towards the reservoir tube but not to extend to the pressure tube. Thus, an opening is left between the baffle spring and the reservoir tube.
While these designs of baffle springs have proven to reduce the amount of aeration in certain applications, there is still uncontrolled damping fluid flow possible between the baffle spring and the reservoir tube which enlarges the oil-gas surface and hence worsens the aeration insensitivity.